1. Field of the Invention
The present invention relates to a heating technology by using a spectral selective type heat radiating material that enables high-efficiency heating to be carried out, and more particularly to a novel type of heating apparatus that uses a heat radiant that radiates infrared radiation in a high-temperature state with high spectral selectivity and high emissivity, having a property capable of easily identifying whether or not the apparatus is operating, and preventing the temperature of the surface of the heat radiant from becoming hotter than required temperature by controlling the spectral selectivity of spectral emissivity, and thereby marked improvements in safety and energy efficiency can be realized.
2. Description of the Related Art
In general, room heating apparatuses can be classified predominantly into radiating type heating apparatuses that use radiation of infrared radiation, hot air current type heating apparatuses that use forced circulation of a hot air current, and convection type heating apparatuses that use both of the above. Moreover, if a method in which the object to be heated is made to be in close contact with a hot object is excluded, then heating apparatuses in factories, farms and the like, and heating apparatuses for drying timber and the like are fundamentally the same as for room heating apparatuses, and can again be classified into the radiating type, the hot air current type, and the convection type. Furthermore, as one type of radiating type heating apparatus, there are apparatuses in which the spectral selective radiant is made small, and a parabolic reflector is used to concentrate the heat radiation in a certain direction, whereby a desired part only is heated locally. Out of the above types of heating apparatus, in the case of a radiating type heating apparatus or a convection type heating apparatus that uses heat radiation, good heat resistance and high infrared emissivity are required of the heat radiating material that radiates infrared radiation in a high-temperature state, and hence a heat-resistant glass or ceramic has been used.
Moving on, the air exists on the Earth generally absorbs infrared radiation, but it is known that the transmittance of infrared radiation is high in a wavelength range of 8 to 13 μm known as the ‘atmospheric window’ (see Solar Energy Utilization Handbook (1985), edited by the Japan Solar Energy Society, p. 45). The absorptance of infrared radiation by the air in wavelength regions other than the ‘atmospheric window’ can be measured using an ordinary infrared spectrophotometer, and upon actually doing this, it was found that the absorption coefficient at a temperature of 30° C. is approximately 1 m−1. This means that most infrared radiation outside the region of the ‘atmospheric window’ does not travel beyond approximately 3 m, but rather is absorbed by the air.
A conventional radiating type heating apparatus or convection type heating apparatus using a heat-resistant glass or ceramic as described above radiates infrared radiation over a broad range from the near infrared region to the far infrared region unselectively. Consequently, in wavelength regions other than the ‘atmospheric window’, depending on the distance to the object to be heated, some of the infrared radiation is absorbed by the air, and heating is realized through heat being supplied to the person or object to be heated indirectly from the air; in the wavelength region of the ‘atmospheric window’, heating is realized through the person or the like receiving radiation directly from the heat radiating material. As a result, even in the case of a heating apparatus that uses a parabolic reflector and thus places importance on directionality, at short distances, the heating effect in which the infrared radiation is received directly will predominate, but at greater distances, there will be a problem that the infrared radiation reaching an object to be heated such as a person from the heating apparatus will only be part of the infrared radiation radiated by the heat radiating material.
As novel heat radiating materials for resolving this problem, spectral selective type heat radiating materials comprising a metal base material and a silicon monoxide film formed thereon are known; such a material selectively radiates infrared radiation in a wavelength range of approximately 8 to 13 μm, which is the ‘atmospheric window’ region in which the air is transparent, and by using such a spectral selective type heat radiating material, it becomes possible to efficiently irradiate infrared radiation onto an object to be heated that is far away.
However, a spectral selective type heat radiating material does not transmit visible light, and barely radiates visible light even when radiating heat, and thus is opaque, and hence it is not easy for a user to know whether or not the heat radiating material is in a high-temperature state, i.e. whether or not the heating apparatus is operating; there is thus a problem that there is a risk of getting burned, which is inadequate from a safety perspective. Moreover, if the same amount of electrical power is put into a material that irradiates infrared radiation unselectively and a spectral selective type heat radiating material, then the spectral selective type heat radiating material will get much hotter, and hence there is a problem that the temperature of the surface of the heat radiant may become excessively high, and thus there is an increased risk of a person or the like getting burned upon accidental contact. In view of the above, even in the case that a spectral selective type heat radiating material is used, if, for example, a heating apparatus for which it can be identified at a glance whether or not the heat radiating material is operating, i.e. a spectral selective type heat radiating material and heating apparatus for which the risk of getting burned or the like is not markedly higher than with a conventional heat radiating material that radiates infrared radiation unselectively, could be developed, then the above problems of a spectral selective type heat radiating material could be resolved.
In view of the prior art described above, the present inventors thus carried out assiduous research with an aim of developing a heating apparatus that uses a spectral selective type heat radiating material, and for which it can easily be identified whether or not the heat radiating material is in a high-temperature state, and moreover the risk of being burned or the like is not markedly greater than with a conventional heating apparatus; as a result, the present inventors succeeded in developing a heating apparatus for which the way of forming spectral selective type heat radiating material film parts is changed, and a heating apparatus and spectral selective type heat radiating material for which the spectral selectivity of spectral emissivity is controlled by adjusting the film thickness, thus accomplishing the present invention.